How to check if you have a virus?

Quick answers

Some quick ways to check if your computer has a virus include running a virus scan, monitoring for unusual behavior like pop-ups or sluggish performance, checking task manager for unfamiliar programs running in the background, and looking for symptoms like unexpected file changes. If you suspect your computer has a virus, stop using it and run a scan with antivirus software immediately.

In today’s digital world, computer viruses are an unfortunate reality. A computer virus is a malicious software program that can spread from one computer to another and disrupt normal functionality or access private information without the owner’s consent. Viruses can infect computers when users open infected email attachments, click on malicious links, or download infected software or files from the internet. Once on a computer, viruses can replicate themselves and cause a range of problems from sluggish performance to complete system failure. Knowing how to check for and remove a computer virus is an important skill for all computer users. This article will provide a comprehensive guide on how to check if your computer has a virus, signs and symptoms to look out for, and steps to take if you confirm your system is infected.

Common ways viruses spread

Before learning how to check for a virus, it’s helpful to understand the most common ways they can infiltrate your computer in the first place:

  • Opening email attachments from unknown senders
  • Visiting compromised websites that trigger malware or virus downloads
  • Downloading infected files or programs from the internet
  • Inserting infected USB flash drives or external hard drives
  • Clicking on pop-up ads or messages
  • Installing unlicensed or pirated software

Being vigilant about these high-risk activities can help prevent virus infections. However, viruses have become increasingly sophisticated and can sometimes infect systems without any action from the user. That’s why it’s critical to routinely check for viruses and run scans even if you don’t notice any obvious problems.

Signs your computer may have a virus

The first step in checking for a virus is watching for telltale signs of an infection:

1. Sluggish computer performance

One of the most common signs is slowed-down computer speed and performance. Things like programs taking longer to open, frequent freezing or crashing, and lagging when browsing the internet point to a possible virus. The reason is that viruses hog system resources to carry out their behind-the-scenes tasks.

2. Pop-up ads and windows

Unexpected pop-up ads, browser windows, and messages can indicate adware or other intrusive infections. Legitimate programs should not cause frequent pop-ups unless initiated by the user.

3. Unusual activity

Strange activity like programs opening on their own, web pages redirecting to unwanted sites, and files going missing or becoming corrupted are all warning signs. Virus infections can disrupt normal computer behavior in unpredictable ways.

4. Computer or browser settings changed

Many viruses alter browser settings like the homepage and default search engine. Unfamiliar toolbars and extensions appearing in your browser can also signal an infection. Outside of your browser, things like your wallpaper, default programs, and startup items changing unexpectedly may point to a virus.

5. Slow or disrupted internet connection

A virus infection can slow your internet speeds to a crawl or even block access altogether. This happens when viruses communicate over the internet to other infected computers or download additional malicious files.

6. Overheating computer

Excessive heat coming from your computer could mean a virus is overloading the processor and hardware by running resource-intensive tasks in the background. Prolonged overheating can lead to permanent damage.

7. Anti-virus software disabled

Some sophisticated viruses target anti-virus programs specifically, stopping them from running or fully disabling them. This prevents detection. If your anti-virus suddenly shuts off and won’t turn back on, it may be compromised by a virus.

8. Suspicious hard drive activity

Hard drive activity lights flickering excessively when no programs are actively running could indicate a virus writing data in the background. Likewise, your hard drive could sound louder than usual as the mechanical parts work harder to carry out virus tasks.

9. Computer freezes or crashes frequently

System freezes, the blue screen of death, and outright crashing are common virus symptoms. Rebooting temporarily alleviates frozen systems but the underlying infection remains.

10. Mysterious network activity

Watch for network traffic during periods of computer inactivity. Viruses communicate over networks and the internet to send data, download files, and spread to other systems. Unusual outbound connections may give away a virus.

How to check for viruses

If you notice any of the warning signs above, your system may well have a virus. But how do you check conclusively? Here are some methods to detect and identify virus infections.

Use antivirus software

The most straightforward way is to run a virus scan using reputable antivirus software like Norton, McAfee, or Avast. Make sure to download the scan from a trusted site, not email links which could be fake. Set your antivirus to run a full system scan which will check all files, folders, and drives connected to your computer. This should detect any known viruses. Schedule regular weekly scans to catch new viruses.

Check task manager for suspicious processes

Open your computer’s task manager (Ctrl + Alt + Del on Windows) and look at all the currently running programs and processes. Sort by CPU or memory usage. Unfamiliar .exe files using high resources could indicate malicious viruses and malware. Research any unknown processes online for more details.

Inspect app permissions

Review installed app permissions in your control panel settings. Malicious apps may request unnecessary permissions like contacts access that could signify viruses. Similarly, browser extensions should only require permissions relevant to their function.

Look for suspicious files

Browse through your files, programs, browser extensions, and other areas viruses hide. Watch for unfamiliar .exe, .dll, .tmp, .vbs, and other suspicious file extensions. Names resembling random characters like “skdjfdk.dll” are red flags. Type these filenames into a search engine to investigate further.

Check hosts file

A common virus technique is modifying the hosts file in Windows located at C:\Windows\System32\Drivers\etc\hosts. Open it in Notepad and look for redirected URLs or IP addresses linking to malicious sites rather than their real destinations.

Reveal hidden files

Make hidden files visible and inspect them – viruses often hide files this way. In Windows 10 open File Explorer, select View > Options > Change folder and search options. Then under the View tab enable “Show hidden files, folders, and drives.”

Use command prompt

Open the command prompt and run “dir /a” to list all files including hidden ones. Type “dir /s” to see files in all subdirectories. Compare the output to a healthy system to spot anomalies.

Check registry for added keys

The Windows registry stores configuration data viruses can modify to launch automatically. Use the Registry Editor to scan for suspicious newly added keys in areas like HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run.

Verify email and website URLs

Carefully inspect hyperlinks in emails and websites before clicking. Hover over them to preview the URLs and look for misspellings or substitutes. Phishing sites impersonate legitimate sites to infect visitors.

Update your operating system

Make sure your OS, software, and security programs are fully patched. Updates often include vital fixes for vulnerabilities that viruses exploit. Turn on automatic updates wherever possible.

Monitor network traffic

Use a packet sniffer tool to log and inspect traffic on your network. Unusual connections to external servers may indicate viruses communicating over the network. Watch for strange data packets being transmitted without your activity.

Check external devices

Don’t overlook external hard drives and USB sticks – these can harbor viruses and automatically infect your computer when plugged in. Scan them with your antivirus before accessing.

Scan with multiple antivirus programs

No single antivirus program catches everything. Run secondary scans with tools like Malwarebytes which uses a different virus definition database. Boot into Safe Mode first to disable any resident viruses.

Reinstall computer operating system

If all else fails, backup your data and perform a clean OS reinstall. This essentially factory resets your computer erasing any viruses or malware. Make sure to delete all your personal files first.

Steps to remove a virus

If your computer is infected, take these steps immediately:

  1. Disconnect from the internet – This prevents spreading and further infection.
  2. Backup important data – Copy personal files to an external drive not infected.
  3. Boot into Safe Mode – Use Safe Mode to load a minimal environment that disables startup programs.
  4. Run a full virus scan – Use reputable antivirus software to scan all files and drives.
  5. Delete or quarantine detected viruses – Follow scan prompts to remove or isolate viruses.
  6. Update antivirus and run another scan – Fully update your virus definitions before doing a re-scan.
  7. Reset browser settings – Viruses often modify browser settings, revert these to defaults.
  8. Change account passwords – Update passwords for any online accounts logged into on the infected computer.
  9. Reconnect drives and devices – Safely reconnect external drives and devices like USBs.
  10. Install OS updates – Make sure your operating system is fully patched.

For severe infections, a full operating system re-installation may be necessary. Save all your data beforehand. Avoid reconnecting the infected system to other devices or networks until it has been completely disinfected to prevent spreading.

How to prevent viruses

Prevention is the best medicine when it comes to computer viruses. Here are proactive measures to improve security:

  • Use antivirus software and keep it updated
  • Don’t open email attachments from unknown senders
  • Watch for phishing scams and suspicious links
  • Only download software from trusted sources like official websites
  • Avoid pirated software, media, and illegal downloads
  • Don’t plug in unrecognized USB drives
  • Regularly backup important data
  • Don’t browse the web as an admin user
  • Be wary of public Wi-Fi hotspots which are common infection points
  • Keep your operating system, browsers, and software updated

Making smart security decisions can go a long way in keeping viruses off your computer. Quickly addressing any infections before they escalate is also key.

Other malware to watch out for

While this guide has focused specifically on computer viruses, there are other types of malicious software (“malware”) that can infect systems in similar ways:


Trojans disguise themselves as legitimate files to trick users into downloading and installing them. They create backdoors for remote access.


Spyware secretly gathers data on users such as internet history, logins, and personal information and transmits it to third parties.


Adware bombards users with constant pop-up advertisements and redirects to try generating revenue from clicks.


Worms self-replicate across networks by exploiting vulnerabilities to spread themselves automatically.


Ransomware encrypts a computer’s files until the user pays a ransom to cybercriminals to decrypt them.


Rootkits conceal themselves deep in operating systems to gain privileged access while cloaking their presence.


Keyloggers record keystrokes such as account usernames and passwords entered on a system.


Botnets link compromised systems together remotely allowing centralized control for malicious activities.

These threats all have different methods of infiltration but many similar motivations and detection techniques. Antivirus software, safe browsing habits, and security awareness provide protection against the wide range of malware that exists.


Viruses and other malware represent a constant danger to computers and users’ privacy and security. But by understanding how viruses work, what signs indicate infection, and using the right tools to scan for and remove threats, you can protect your system. Implementing vigilant browsing, downloading, and security practices also offers strong preventative defense against viruses taking hold in the first place. Keeping comprehensive backups provides insurance against data loss from infections. With the right knowledge and procedures, you can avoid viruses wreaking havoc on your computer and network.